Can't see through BSDF principled/glass 2.8
You can't see through any shader that was opaque.



The BSDF shader work on Surface Only, as Blender is a surface mesh 3D tool.

If you assign a opaque color to inner surface, the glass BSDF will become useless since you are literally painting the inner glass with that color.

A better approach will be adding a surface on the liquid surface, and change that surface color. Also blend shader with Glass or other transparent shader to make better.